In addition to the commonly known semiconductor devices like diodes and transistors, there are other devices too which are manufactured using semiconductor materials. The semiconductor technology is used in varactors which are a kind of metal-insulator variable capacitors and modulators. These two semiconductor devices are reviewed in detail below:
Varactor is a semi conductor device which is used to store charge at the interface of the two insulators. Thus, it acts as a variable capacitor and that is why it is named as a varactor. When a current is passed to shift the diode used to create varactor semi conductor device from its flat-band condition to forward bias, charge can be stored in the region between the two insulators. Since the charge is dependent upon the applied voltage, the device acts as a varactor. Like in case of standard capacitor, the varactors acting as charge storage devices gives rise to capacitance.
The other semiconductors device, the review of which is featured in this article is known as modulator. Modulator is defined as a device which has the ability of modulating a broad range of wavelengths from millimeter wave through infrared. The semiconductor devices and metal-insulator devices can also be use as modulators. These semi conductor devices work on the principle which is based on the effects of matching an antenna and load. When an antenna and load are matched the absorbed power is at a maximum, and the reflected or transmitter power is at a minimum. Alternatively, when there is significant mismatch between the antenna and load, the reflected or transmitted power increases. Modulation is modeled by biasing the diode in a detector design to change the impedance match of the diode and antenna.
Since, a diode manufactured using the MIIM diode is highly nonlinear, its differential resistance is very much different at a low voltage, say it is equal to 0.3 volts and at a higher voltage of 0.4 volts. Thus, when the applied voltage to the diode, the match to the antenna changes, which is used to modulate the incoming radiation.